diff --git a/.github/workflows/dockerfile.yaml b/.github/workflows/dockerfile.yaml
index 9669ef5bd6..4cada19834 100644
--- a/.github/workflows/dockerfile.yaml
+++ b/.github/workflows/dockerfile.yaml
@@ -104,18 +104,22 @@ jobs:
         id: list-changed
         run: |
           changed=$(ct list-changed --chart-dirs kubernetes/chart \
-                                    --target-branch ${{ github.event.repository.default_branch }})
+                                    --target-branch "$DEFAULT_BRANCH")
           if [[ -n "$changed" ]]; then
             echo "changed=true" >> "$GITHUB_OUTPUT"
           fi
+        env:
+          DEFAULT_BRANCH: ${{ github.event.repository.default_branch }}
 
       - name: Run chart-testing (lint)
         if: steps.list-changed.outputs.changed == 'true'
         run: |
           ct lint --github-groups \
                   --chart-dirs kubernetes/chart \
-                  --target-branch ${{ github.event.repository.default_branch }} \
+                  --target-branch "$DEFAULT_BRANCH" \
                   --lint-conf lintconf.yaml
+        env:
+          DEFAULT_BRANCH: ${{ github.event.repository.default_branch }}
 
       - name: Create kind cluster
         uses: helm/kind-action@v1